Using R for Introductory Statistics, 3.1

Pairs of categorical data

The grades data.frame holds two columns of letter grades, giving pairs of categorical data, like so:

prev grade
1 B+ B+
2 A- A-
3 B+ A-
...
122 B B

This type of data can be summarized by the table function, which counts the occurrence of each possible pair of letter grades. But first, I was never a fan of plus-minus grading, so lets do away with that.